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The internal and external radius of a hemisphere are r and R respectively.Find the total surface area of the solid. Now this all seems to be very easy as CSA of this hemisphere=2*pi*r^2+2*pi*R^2 what i cannot find out is the reaming area.

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Hint: The "flat" part lies in a plane, and consists of a disk of radius $R$ with a disk of radius $r$ removed from its center. What's the area of the resulting annular region?

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  • $\begingroup$ u see then its 2*pi*(R-r)^2=the area of the resulting annular region $\endgroup$
    – Pole_Star
    Feb 8, 2017 at 13:47

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